Method of resolving overlaps in data transmission and user equipment therefor

ABSTRACT

A method of a user equipment (UE) operating in a wireless communication system using orthogonal subcarriers, the method including generating, by the UE, Orthogonal Frequency Division Multiplexing (OFDM)-based symbols, wherein each OFDM-based symbol includes a cyclic prefix (CP) and a data part, transmitting, by the UE, a first subframe including N OFDM-based symbols, wherein N is an integer and transmitting, by the UE, a second subframe including N OFDM-based symbols, following the first subframe, wherein, when the first subframe and the second subframe are overlapped based on a timing adjustment command received from a base station, the first subframe is transmitted completely while the second subframe is transmitted partially without an overlapped part of the second subframe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/231,290 filed on Aug. 8, 2016, which is a Continuation of U.S. patentapplication Ser. No. 14/280,375 filed May 16, 2014 (now U.S. Pat. No.9,432,993 issued Aug. 30, 2016), which is a Continuation of U.S. patentapplication Ser. No. 12/686,325 filed Jan. 12, 2010 (now U.S. Pat. No.8,767,706, issued Jul. 1, 2014), which is a Continuation of U.S. patentapplication Ser. No. 12/350,985 filed on Jan. 9, 2009 (now U.S. Pat. No.7,672,339, issued Mar. 2, 2010), which claims priority to Korean patentapplication No. 10-2008-0003517 filed on Jan. 11, 2008, the entirecontents of all of the above applications are hereby incorporated byreference into the present application.

BACKGROUND OF THE INVENTION

The present invention relates to an orthogonal frequency divisionmultiple access (OFDMA) and analogous radio access scheme, and moreparticularly, to a method of adjusting transmission timing at atransmitting side, a method of transmitting continuous packets, and amobile station thereof.

In the basic principle of orthogonal frequency division multiplexing(OFDM), a data stream having a high rate is divided into a large numberof data streams having a slow rate and the data streams aresimultaneously transmitted using a plurality of carriers. Each of theplurality of carriers is called a sub-carrier. Since orthogonalityexists among the plurality of carriers in the OFDM, the carriers can bedetected by a receiving side although frequency components of thecarriers overlap with each other. The data stream having the high rateis converted into a plurality of data streams having the slow rate by aserial-to-parallel converter, each of the plurality of data streamsconverted in parallel is multiplied by each of the sub-carriers, thedata streams are added, and the added data streams are transmitted tothe receiving side.

The plurality of parallel data streams generated by theserial-to-parallel converter may be transmitted by the plurality ofsub-carriers using an Inverse Discrete Fourier Transform (IDFT), and theIDFT may be efficiently implemented using an Inverse Fast FourierTransform (IFFT).

Since a symbol duration of each of the sub-carriers having the slow rateis increased, a relative signal dispersion on a time axis, which isgenerated by multi-path delay spread, is decreased. Inter-symbolinterference can be reduced by inserting a guard interval longer thanthe delay spread of a channel between OFDM symbols. In addition, when apart of an OFDM signal is copied and arranged at a start part of asymbol in a guard interval, OFDM symbols are cyclically extended suchthat the symbols are protected.

Meanwhile, OFDMA is a multiple access method which provides a part ofavailable sub-carriers to each user in a system using OFDM modulationmethod so as to realize multiple access. In the OFDM, each of frequencyresources called sub-carriers is provided to each user. That is, thefrequency resources are independently provided to the plurality of usersso as not to overlap with each other. As a result, the frequencyresources are exclusively allocated.

FIG. 1 is a view showing the structure of a transmitting side using asingle carrier-frequency division multiple access (SC-FDMA) scheme.

The SC-FDMA (IFDMA or DFTs-OFDMA) scheme which is a modified example ofthe OFDMA may be considered for uplink wideband transmission. In theSC-FDMA scheme, discrete Fourier Transform (DFT) coding is performedwith respect to symbols before OFDMA modulation and multiplexing.Accordingly, input symbols are spread over the entire transmission bandin a frequency domain, a peak-to-average power ratio (PAPR) of a lastlytransmitted signal decreases, and the required operation range of atransmitting amplifier of a mobile station can be reduced.

However, if transmission timing of a packet is adjusted and moreparticularly if packet transmission timing is advanced while atransmitting side continuously transmits packets by using the abovemodulation method two continuous packets may collide.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of adjustingtransmission timing at a transmitting side which is capable ofpreventing deterioration in reception performance and minimizingreception complexity when the transmitting side changes the transmissiontiming in a wireless communication that uses a cyclic prefix (CP) forpreventing deterioration in reception performance due to delay spread ortiming misalignment.

Another object of the present invention is to provide a method ofcontinuously transmitting packets by using the method of adjusting thetransmission timing.

A further object of the present invention is to provide a mobile stationto which the method of transmitting the continuous packets is applied.

The object of the present invention can be achieved by providing amethod of adjusting transmission timing, the method including: adjustingthe transmission timing according to a transmission timing adjustmentcommand when the transmission timing adjustment command is received froma receiving side; and creating a cyclic prefix (CP) in consideration ofa part of a CP of a next symbol which overlaps with a previous symbol ona time axis on the basis of the adjusted transmission timing.

The CP may be designed to have various lengths in consideration ofchannel conditions. For simplicity, the CP may be designed to have twodifferent lengths, i.e., a normal CP and an extended CP. For example, in3GPP LTE system using 20 MHz bandwidth, one symbol consists of 2048samples and each symbol has duration of 66.67 us. In theseconfigurations, the normal CP consists of 144 or 160 samples, wherebychannel delay of 4.69 or 5.2 us can be covered. And, the extended CPconsists of 512 samples, whereby channel delay of 16.67 us can becovered.

The adjusting of the transmission timing may include advancing starttiming of a subframe transmitted by a mobile station while the mobilestation continuously transmits packets.

In the creating of the CP, a part overlapping with the previous symbolmay be removed from the CP extracted from data to be transmitted by themobile station.

In the creating of the CP, the CP of the length, which is left byexcluding a part overlapping with the previous symbol from apredetermined length, may be extracted from data to be transmitted bythe mobile station.

In another aspect of the present invention, provided herein is a methodof transmitting continuous packets, the method including: adjustingtransmission timing according to a transmission timing adjustmentcommand when the transmission timing adjustment command is received froma receiving side; creating a cyclic prefix (CP) in consideration of apart of a CP of a next symbol which overlaps with a previous symbol on atime axis on the basis of the adjusted transmission timing; andcontinuously transmitting a next symbol including the created CP.

The adjusting of the transmission timing may include advancing starttiming of a subframe transmitted by a mobile station while the mobilestation continuously transmits packets. In the creating of the CP, apart overlapping with the previous symbol may be removed from the CPextracted from data to be transmitted by the mobile station.

In the creating of the CP, the CP of the length, which is left byexcluding a part overlapping with the previous symbol from apredetermined length, may be extracted from data to be transmitted bythe mobile station.

In another aspect of the present invention, provided herein is a mobilestation including: a cyclic prefix (CP) insertion unit creating a CP inconsideration of a part of a CP of a next symbol which overlaps with aprevious symbol on a time axis on the basis of the adjusted transmissiontiming when transmission timing is adjusted according to a transmissiontiming adjustment command while subframes are transmitted continuously;and a wireless communication unit continuously transmitting a nextsymbol including the created CP.

The CP insertion unit may remove a part overlapping with the previoussymbol from the CP extracted from data transmitted by the mobile stationand insert the CP into the next symbol. The CP insertion unit mayextract a CP of the length, which is left by excluding the partoverlapping with the previous symbol from a predetermined length, fromthe data to be transmitted by the mobile station and insert theextracted CP into the next symbol.

According to the embodiments of the present invention, it is possible toprevent deterioration in reception performance and minimize receptioncomplexity even when packet transmission timing is adjusted at atransmitting side using an OFDMA or analogous radio access scheme.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a view showing the structure of a transmitting side using asingle carrier-frequency division multiple access (SC-FDMA) scheme.

FIG. 2 is a view showing a process of adjusting transmission timing on atime axis at a transmitting side.

FIG. 3 is a view showing a process of adjusting transmission timing on atime axis while a transmitting side transmits packets continuously.

FIG. 4 is a view showing a case where a collision part of a previoussymbol is not transmitted in order to avoid collision shown in FIG. 3 .

FIG. 5 is a flowchart illustrating a method of adjusting transmissiontiming according to an embodiment of the present invention.

FIG. 6 is a flowchart illustrating a method of continuously transmittingpackets according to an embodiment of the present invention.

FIG. 7 is a view showing a transmitting side and a receiving sideaccording to an embodiment of the present invention.

FIG. 8 is a view showing a process of continuously transmitting packetsaccording to the method of FIG. 6 .

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. However, the following embodiments of the present inventionmay be variously modified and the range of the present invention is notlimited to the following embodiments.

Symbols described herein include OFDM symbols and SC-FDMA symbols. Forconvenience of description, the OFDM symbols will be described.

In uplink of a cellular mobile communication system using a multiplexingscheme such as an OFDMA or SC-FDMA scheme, OFDM symbols transmitted bydifferent mobile stations in a cell at the same time are considered. Thereception timings of the OFDM symbols at a base station should be equalwithin at least a CP length. In only this case, the base station candemodulate the OFDM symbols transmitted via different frequency bands bythe different mobile stations at the same time without interference.

In addition, although it is assumed that only one mobile station existswithin a cell, if an error occurs between periods of an oscillator inthe mobile station used for creating an uplink transmission signal andan oscillator in the base station used for receiving the uplink signal,an error between a transmission signal creating timing of the mobilestation and a reception timing of the base station may be increased withtime.

Accordingly, the base station transmits transmission timing adjustmentcommands to the mobile stations within the cell periodically or whennecessary. By this command, the base station can advance or delay thetransmission timing of each mobile station by one or more predeterminedsteps. In addition, the base station adjusts reception timing of thesignal that is transmitted by each mobile station.

The adjustment of the transmission timing is performed in the unit ofpacket transmission times constituted by a plurality of OFDM symbols,that is, in the unit of subframes. In other words, the adjustment of thetransmission timing indicates an operation for advancing or delaying thesubframe by one or more steps on a time axis.

FIG. 2 is a view showing a process of adjusting transmission timing on atime axis at a transmitting side.

FIG. 2 shows an example when the transmitting side does not continuouslytransmit packets. If transmission timing adjustment command is receivedafter the transmission of a series of subframes is completed, a subframestart timing is adjusted before the transmission of the subframe isnewly started. In this case, collision between symbols does not occur.

FIG. 3 is a view showing a process of adjusting transmission timing on atime axis while a transmitting side transmits continuous packets.

As shown in FIG. 3 , when the transmission timing adjustment commandreceived from the receiving side is applied while the transmitting sidecontinuously transmits the packets and, more particularly, when thepacket transmission timing is advanced, a part in which two continuouspackets collide occurs. That is, a last OFDM symbol of a previous packetand a first OFDM symbol of a next packet overlap with each other for theadjustment of the transmission timing.

If the signals of the overlapped part are combined and transmittedtogether in order to avoid inter-symbol collision, interference occursin a part in which the previous OFDM symbol and the next OFDM symboloverlap with each other and thus reception performance deteriorates.

FIG. 4 is a view showing a case where a part of a previous symbol in acollision part is not transmitted in order to avoid collision shown inFIG. 3 .

In FIG. 4 , the transmitting side does not transmit a signal of anoverlapped part of a previous OFDM symbol. In this case, if thereceiving side does not adjust the reception timing with respect to theprevious OFDM symbol in advance, the overlapped part of the signal ofthe previous OFDM symbols is lost and thus the reception performance ofthe previous OFDM symbol deteriorates.

Accordingly, in the embodiments of the present invention, the signalcorresponding to the overlapped part of a next OFDM symbol is nottransmitted.

FIG. 5 is a flowchart illustrating a method of adjusting transmissiontiming according to an embodiment of the present invention.

First, it is determined whether transmission timing adjustment commandis received from a receiving side while packets are transmittedcontinuously (S510). At this time, if the transmission timing adjustmentcommand is not received, a CP is created (S540). In this step, thecreated CP is a complete CP. The created CP may be a normal CP or anextended CP.

If the transmission timing adjustment command is received, transmissiontiming is adjusted according to the transmission timing adjustmentcommand (S520).

Next, a CP is created in consideration of a part of a CP of a nextsymbol which overlaps with a previous symbol on a time axis on the basisof the transmission timing adjusted by the transmitting side (S530). Thecreated CP is inserted into a foremost symbol of packets which will becontinuously transmitted. Preferably, the CP may be created by a methodof removing a part overlapping with the previous symbol from the CPextracted from data to be transmitted by a mobile station. Preferably,the CP may be created by a method of extracting a CP of the length,which is left by excluding a part overlapping with the previous symbolfrom a predetermined length, from data to be transmitted by the mobilestation.

FIG. 6 is a flowchart illustrating a method of continuously transmittingpackets according to an embodiment of the present invention.

First, it is determined whether transmission timing adjustment commandis received from a receiving side while packets are transmittedcontinuously (S610). At this time, if the transmission timing adjustmentcommand is not received, a CP is created (S640). In this step, thecreated CP is a complete CP. The created CP may be a normal CP or anextended CP. The created CP is inserted into a foremost symbol ofpackets to be continuously transmitted.

If the transmission timing adjustment command is received from thereceiving side, transmission timing is adjusted according to thetransmission timing adjustment command (S620).

Next, a CP is created in consideration of a part of a CP of a nextsymbol which overlaps with a previous symbol on a time axis on the basisof the transmission timing adjusted by the transmitting side (S630). Thecreated CP is inserted into a foremost symbol of packets to becontinuously transmitted.

Next, the next symbol including the created CP is continuouslytransmitted to the receiving side by the packets (S650).

Finally, if a buffer in which data to be transmitted by a transmittingside is stored is empty, a packet transmitting process is completed and,if the buffer is not empty, it is determined whether the transmissioncommand adjustment command is received while transmitting the packetscontinuously (S610).

FIG. 7 is a view showing a transmitting side and a receiving sideaccording to an embodiment of the present invention.

The transmitting side 710 includes a symbol generator 714 having amodulator/demodulator 713, a CP insertion unit 711 and a wirelesscommunication unit 712. The modulator/demodulator 713 delivers symbols715, which are created by applying a modulation scheme such as an OFDMAscheme or a SC-FDMA scheme, to the CP insertion unit 711.

When the transmission timing is adjusted according to the transmissiontiming adjustment command while subframes are transmitted continuously,the CP insertion unit 711 creates a CP in consideration of a part of aCP of a next symbol which overlaps with a previous symbol on a time axison the basis of the adjusted transmission timing. Preferably, the CPinsertion unit 711 may remove the part overlapping with the previoussymbol from the CP extracted from data to be transmitted by thetransmitting side 710, and insert the CP into a next symbol. Preferably,the CP insertion unit 711 may extract a CP of the length, which is leftby excluding the part overlapping with the previous symbol from apredetermined length, from the data to be transmitted by thetransmitting side and insert the extracted CP into the next symbol.

The wireless communication unit 712 receives the transmission timingadjustment command from the receiving side 720. The wirelesscommunication unit 712 continuously transmits the next symbol includingthe CP created by the CP insertion unit 711 to the receiving side 720.

FIG. 8 is a view showing a process of continuously transmitting packetsaccording to the method of FIG. 6 .

In FIG. 8 , when the signal transmission parts of two packets overlapwith each other by the adjustment of the transmission timing at thetransmitting side, a signal of an overlapped part, including a CP, of anext packet in the two packets overlapping with each other on the timeaxis is not transmitted. At this time, if a part of a next OFDM symbolwhich overlaps with a previous OFDM symbol is included in a CP and thedelay spread of a channel is not large, the previous OFDM symbol and thenext OFDM symbol can be received without deterioration in receptionperformance.

The above embodiments are provided by combining components and featuresof the present invention in specific forms. The components or featuresof the present invention should be considered optional if not explicitlystated otherwise. The components or features may be implemented withoutbeing combined with other components or features. The embodiments of thepresent invention may also be provided by combining some of thecomponents and/or features. The order of the operations described abovein the embodiments of the present invention may be changed. Somecomponents or features of one embodiment may be included in anotherembodiment or may be replaced with corresponding components or featuresof another embodiment. It will be apparent that claims which are notexplicitly dependent on each other can be combined to provide anembodiment or new claims can be added through amendment after thisapplication is filed.

The above embodiments of the present invention have been describedfocusing mainly on the data communication relationship between a mobilestation and a Base Station (BS). Specific operations which have beendescribed as being performed by the BS may also be performed by uppernodes as needed. That is, it will be apparent to those skilled in theart that the BS or any other network node may perform various operationsfor communication with terminals in a network including a number ofnetwork nodes including BSs. The term “base station (BS)” may bereplaced with another term such as “fixed station”, “Node B”, “eNode B(eNB)”, or “access point”. The term “mobile station” may also bereplaced with another term such as “user equipment (UE)”, “terminal”, or“mobile subscriber station (MSS)”.

The embodiments of the present invention can be implemented by hardware,firmware, software, or any combination thereof. Various embodiments ofthe present invention may be implemented by one or more applicationspecific integrated circuits (ASICs), digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, or the like.

Various the embodiments of the present invention may also be implementedin the form of software modules, processes, functions, or the like whichperform the features or operations described above. Software code can bestored in a memory unit so that it can be executed by a processor. Thememory unit may be located inside or outside the processor and cancommunicate data with the processor through a variety of known means.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

The present invention provides a method of adjusting transmission timingat a transmitting side, which is capable of preventing deterioration inreception performance and minimizing reception complexity, a method oftransmitting continuous packets, and a mobile station thereof. Thepresent invention is applicable to a device used in an OFDMA andanalogous radio accessing scheme, such as a mobile station or a basestation, and a transmission/reception algorithm.

What is claimed is:
 1. A method performed by a mobile device in awireless communication system, the method comprising: receiving, from abase station, a timing adjustment command for adjusting a transmissiontiming; and performing a first uplink transmission through a firstuplink time unit including a plurality of symbols, wherein each of theplurality of symbols includes a cyclic prefix, wherein a transmissiontiming of the first uplink time unit is advanced according to the timingadjustment command, and wherein based on the first uplink time unitoverlapping, due to the timing adjustment command, with a second uplinktime unit through which a second uplink transmission is performed, (i) aformer time unit among the first uplink time unit and the second uplinktime unit is transmitted completely, and (ii) a latter time unit amongthe first uplink time unit and the second uplink time unit is reduced induration so as to be transmitted without a part overlapped with theformer time unit.
 2. The method of claim 1, wherein the latter time unitis the first uplink time unit to which the timing adjustment command isapplied.
 3. The method of claim 1, wherein a duration of the overlappedpart between the former time unit and the latter time unit is greaterthan a duration of the cyclic prefix of the latter time unit.
 4. Themethod of claim 1, wherein each symbol further includes a data part, andthe data part is located after the corresponding cyclic prefix of thesymbol.
 5. The method of claim 1, wherein the symbols include orthogonalfrequency division multiplexing (OFDM) symbols or singlecarrier-frequency division multiple access (SC-FDMA) symbols.
 6. Themethod of claim 1, wherein at least the first uplink transmission or thesecond uplink transmission includes a data transmission.
 7. The methodof claim 6, wherein each of the first uplink transmission and the seconduplink transmission includes a respective data transmission.
 8. Themethod of claim 1, wherein the overlapped part without which the lattertime unit is transmitted includes at least a part of a cyclic prefix ofa starting symbol of the latter time unit.
 9. A mobile device configuredto operate in a wireless communication system, the mobile devicecomprising: a transceiver; at least one processor; and at least onecomputer memory operably connectable to the at least one processor andstoring instructions that, when executed by the at least one processor,perform operations comprising: receiving, from a base station throughthe transceiver, a timing adjustment command for adjusting atransmission timing, and performing a first uplink transmission througha first uplink time unit including a plurality of symbols, wherein eachof the plurality of symbols includes a cyclic prefix, wherein atransmission timing of the first uplink time unit is advanced accordingto the timing adjustment command, and wherein based on the first uplinktime unit overlapping, due to the timing adjustment command, with asecond uplink time unit through which a second uplink transmission isperformed, (i) a former time unit among the first uplink time unit andthe second uplink time unit is transmitted completely, and (ii) a lattertime unit among the first uplink time unit and the second uplink timeunit is reduced in duration so as to be transmitted without a partoverlapped with the former time unit.
 10. The mobile device of claim 9,wherein the latter time unit is the first uplink time unit to which thetiming adjustment command is applied.
 11. The mobile device of claim 9,wherein a duration of the overlapped part between the former time unitand the latter time unit is greater than a duration of the cyclic prefixof the latter time unit.
 12. The mobile device of claim 9, wherein eachsymbol further includes a data part, and the data part is located afterthe corresponding cyclic prefix of the symbol.
 13. The mobile device ofclaim 9, wherein the symbols include orthogonal frequency divisionmultiplexing (OFDM) symbols or single carrier-frequency divisionmultiple access (SC-FDMA) symbols.
 14. The mobile device of claim 9,wherein at least the first uplink transmission or the second uplinktransmission includes a data transmission.
 15. The mobile device ofclaim 14, wherein each of the first uplink transmission and the seconduplink transmission includes a respective data transmission.
 16. Themobile device of claim 9, wherein the overlapped part without which thelatter time unit is transmitted includes at least a part of a cyclicprefix of a starting symbol of the latter time unit.